1. Field of the Invention
The present invention relates to a recording apparatus for recording information using mark formation performed by focusing a first light beam at a given position in a recording layer included in an optical disc recording medium with an objective lens, and a control method used in the recording apparatus.
2. Description of the Related Art
As optical recording media for recording and reproducing signals by light illumination, for example, so-called optical discs such as CDs (Compact Discs), DVDs (Digital Versatile Discs), and BDs (Blu-ray Discs: trade mark) have been popularized.
With regard to the next-generation optical recording media of the currently popularized optical recording media such as CDs, DVDs, and BDs, first, the applicant has previously proposed a so-called bulk recording-type optical medium as disclosed in Japanese Unexamined Patent Application Publication No. 2008-135144 and Japanese Unexamined Patent Application Publication No. 2008-176902.
Here, bulk recording is, for example, a technique for performing multi-layer recording in a bulk layer 102 by performing laser light illumination while sequentially changing focal positions in an optical recording medium (a bulk-type recording medium 100) having at least a cover layer 101 and the bulk layer (recording layer) 102 as illustrated in FIG. 13, thereby achieving an increase in recording capacity.
For the bulk recording, in Japanese Unexamined Patent Application Publication No. 2008-135144, a recording technique called a microhologram method is disclosed.
The microhologram method is, as illustrated in FIGS. 14A and 14B, mainly classified into a positive-type microhologram method and a negative-type microhologram method.
In the microhologram method, as a recording material of the bulk layer 102, a so-called hologram recording material is used. As the hologram recording material, for example, photopolymerizable polymer or the like is widely used.
The positive-type microhologram method is, as illustrated in FIG. 14A, a technique for condensing two opposing beams (beam A and beam B) at the same position to form a fine fringe (hologram) which becomes a recording mark.
In addition, the negative-type microhologram method illustrated in FIG. 14B is, in the idea reverse to the positive-type microhologram method, a technique for erasing a fringe which is formed in advance using laser light illumination to use the erasure portion as a recording mark.
FIGS. 15A and 15B are diagrams for explaining the negative-type microhologram method.
In the negative-type microhologram method, before performing a recording operation, as illustrated in FIG. 15A, an initialization process for forming a fringe in the bulk layer 102 is performed in advance. Specifically, as illustrated in FIG. 15A, beams C and D are illuminated by parallel light to be opposed to form the fringes on the entirety of the bulk layer 102.
As such, after the fringe is formed in advance by the initialization process, information recording is performed by forming erasure marks as illustrated in FIG. 15B. Specifically, by performing laser light illumination according to the recording information in a state where laser beams are focused at an arbitrary layer position, the information recording using erasure marks is performed.
In addition, the applicant also proposes, as a bulk recording technique different from the microhologram method, a recording technique for forming voids (holes) as recording marks, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902.
The void recording method is a technique for performing laser light illumination on the bulk layer 102 made of a recording material such as photopolymerizable polymer at a relatively high power, thereby recording holes (voids) in the bulk layer 102. As disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902, the hole portions formed as described above become portions having different refractive indexes from other portions in the bulk layer 102, and reflectance of light at the boundaries thereof can be enhanced. Therefore, the hole portions function as recording marks, thereby implementing information recording using the formation of hole marks.
In such void recording methods, since holograms are not formed, recording is done when light illumination is performed on one side. That is, unlike the positive-type microhologram method, two beams are not condensed at the same position to form recording marks.
In addition, in comparison to the negative-type microhologram method, there is an advantage in that an initialization process is not performed.
Moreover, in Japanese Unexamined Patent Application Publication No. 2008-176902, an example in which light for pre-curing before recording is illuminated when void recording is to be performed is described. However, recording of voids can be made even when illumination of light for pre-curing is omitted.
However, although various recording techniques as described above have been proposed for bulk recording-type (simply referred to as bulk-type) optical disc recording media, a recording layer (bulk layer) of such a bulk-type optical disc recording medium does not have an explicit multi-layer structure in the sense that, for example, a plurality of reflection films are formed. That is, the bulk layer 102 is not provided with a reflection film and a guiding groove that a typical multi-layer disc has, for each recording layer.
Therefore, in the structure of the bulk-type recording medium 100 illustrated in FIG. 13 as it is, during recording without marks being formed, focus servo or tracking servo may not be performed.
Accordingly, in practice, the bulk-type recording medium 100 is provided with a reflection surface (reference surface) which is the reference to have a guiding groove as illustrated in FIG. 16.
Specifically, guiding grooves (position guiding elements) such as pits or grooves are formed on a lower surface side of the cover layer 101, and a selective reflection film 103 is formed thereon. In addition, on the lower side of the cover layer 101 on which the selective reflection film 103 is formed, as an intermediate layer 104 in FIG. 16, for example, the bulk layer 102 is laminated with an adhesive material such as UV-curable resin.
In addition, in this medium structure, the bulk-type recording medium 100 is, as illustrated in FIG. 17, illuminated with a second laser light as a laser light for position control separately from a laser light (first laser light) for recording (or reproducing) marks.
As illustrated in FIG. 17, the first and second laser lights illuminate the bulk-type recording medium 100 via a common objective lens.
Here, if the second laser light reaches the bulk layer 102, there is a concern that the second laser light has an adverse effect on mark recording in the bulk layer 102. Accordingly, in a bulk recording method according to the related art, a laser light having a wavelength band different from that of the first laser light is used as the second laser light, and the selective reflection film 103 which has wavelength selectivity in that it reflects the second laser light and transmits the first laser light is provided as a reflection film formed on a guide groove formation surface (reference surface).
On the above-described premise, operations performed during mark recording in the bulk-type recording medium 100 will be described with reference to FIG. 17.
First, when multi-layer recording is to be performed on the bulk layer 102 without a guiding groove or a reflection film being formed, which layer position marks have to be recorded in the bulk layer 102 in a depth direction is set in advance. In the FIG. 17, a case is exemplified where as layer positions at which the marks are to be formed (mark formation layer: also called an information recording layer) in the bulk layer 102, first to fifth information recording layers L1 to L5, totaling 5 information recording layers (mark formation layers) L, are set. As illustrated in FIG. 17, the layer position of the first information recording layer L1 is set to a position at a first offset of of-3 L1 in a focus direction (depth direction) from the selective reflection film 103 (reference surface) provided with guiding grooves. In addition, the layer positions of the second, third, fourth, and fifth information recording layers L2, L3, L4, and L5 are respectively set to positions at second, third, fourth, and fifth offsets of of-L2, of-L3, of-L4, and of-L5 from the selective reflection film 103.
During recording in which marks are not formed yet, focus servo or tracking servo may not be performed on the layer positions as objects in the bulk layer 102 on the basis of reflected light of the first laser light. Therefore, during recording, focus servo control and tracking servo control of the objective lens are performed on the basis of the reflected light of the second laser light as a position control light so that the spot position of the second laser light follows the guiding grooves on the selective reflection film 103.
However, the first laser light which is a mark recording light has to reach the bulk layer 102 formed under the selective reflection film 103. Accordingly, in this optical system, separately from a focus mechanism of the objective lens, a first laser focus mechanism is provided for individually adjusting a focal position of the first laser light.
Here, an internal configuration example of the recording apparatus of the bulk-type recording medium 100 including the mechanism for individually adjusting the focal position of the first laser light is illustrated in FIG. 18.
In FIG. 18, a first laser diode 111 denoted by LD1 in FIG. 18 is a light source of the first laser light, and a second laser diode 119 denoted by LD2 is a light source of the second laser light. As understood from the above description, the first and second laser diodes 111 and 119 respectively are adopted to emit laser lights having wavelength bands different from each other.
As illustrated in FIG. 18, the first laser light emitted by the first laser diode 111 is incident on the first laser focus mechanism constituted by a fixed lens 113, a movable lens 114, and a lens driving unit 115 via a collimation lens 112. As the movable lens 114 is driven by the lens driving unit 115 in a direction parallel to an optical axis of the first laser light, collimation of the first laser light incident on an objective lens 117 in FIG. 18 is changed, so that the focal position of the first laser light can be adjusted separately from a change in focal position that is caused by driving the objective lens 117.
The first laser light transmitted via the first laser focus mechanism is incident on a dichroic mirror 116 adopted to transmit light having the same wavelength band as that of the first laser light and reflect light having different wavelength bands.
As illustrated in FIG. 18, the first laser light transmitting the dichroic mirror 116 illuminates the bulk-type recording medium 100 via an objective lens 118. The objective lens 117 is held to be displaced in the focus direction and a tracking direction by a biaxial actuator 118.
In addition, the second laser light emitted by the second laser diode 119 transmits a beam splitter 121 via the collimation lens 120 and is incident on the above-mentioned dichroic mirror 116. The second laser light reflects from the dichroic mirror 117 and is incident on the objective lens 117 so that its optical axis is aligned with the optical axis of the first laser light transmitting the dichroic mirror 116.
The second laser light incident on the objective lens 117 is focused on the selective reflection film 103 (reference surface) of the bulk-type recording medium 100 as the biaxial actuator 118 is driven under focus servo control by a servo circuit 125 described later.
The reflected light of the second laser light from the selective reflection film 103 is reflected from the dichroic mirror 116 via the objective lens 117 and is then reflected again from the beam splitter 121. The reflected light of the second laser light from the beam splitter 121 is condensed on a detection surface of a photodetector 123 via a condenser lens 122.
A matrix circuit 124 generates focusing and tracking error signals on the basis of light sensing signals detected by the photodetector 123 and supplies the error signals to the servo circuit 125.
The servo circuit 125 generates a focus servo signal and a tracking servo signal from the error signals. As the above-mentioned biaxial actuator 118 is driven on the basis of the focus servo signal and the tracking error signal, the focus servo control and the tracking servo control of the objective lens 117 are realized.
In the recording apparatus illustrated in FIG. 18, when mark recording is performed on the given information recording layer L as an object selected from among the information recording layers L set in advance in the bulk-type recording medium 100, the operation of the lens driving unit 115 is controlled to change the focal position of the first laser light by an amount of the offset of corresponding to the selected information recording layer L.
Specifically, setting of such an information recording position is controlled by, for example, a controller 126 that controls the entire recording apparatus. That is, the operation of the lens driving unit 115 is controlled by the controller 126 on the basis of an amount of the offset of-Lx set in advance according to the information recording layer Lx as an object, thereby setting the information recording position (focal position) of the first laser light to the information recording layer Lx which is the object.
In addition, just for confirmation, the tracking servo of the first laser light during recording is, as described above, automatically performed as the servo circuit 125 performs the tracking servo control of the objective lens 117 on the basis of the reflected light of the second laser light.
Moreover, when the bulk-type recording medium 100 on which the mark recording is performed in advance is reproduced, the position of the objective lens 117 may not be controlled on the basis of the reflected light of the second laser light unlike during recording. That is, during reproduction, the focus servo control and the tracking servo control of the objective lens 117 may be performed on mark rows as objects formed on the information recording layer L as a reproduction object, on the basis of the reflected light of the first laser light.
As described above, in the bulk recording method, in the bulk-type recording medium 100, the first laser light as the mark recording light and the second laser light as the position control light are illuminated via the common objective lens 117 (to be combined in the same optical axis). Thereafter, the focus servo control and the tracking servo control of the objective lens 117 are performed on the basis of the reflected light of the second laser light, so that the focus servo and the tracking servo of the first laser light can be performed even though the guiding grooves are not formed on the bulk layer 102.